[esp/scene] Added loading of Gibson Semantics scene if MP3D semantic is missing, integration test

[mathfac]

Motivation and Context

With current code state 3dscenegraph semantic annotation files (*.scn) won't load, as our semantic loading pipeline triggers only on *.house files. To enable functionality implemented in #393 and #374 added loading of Gibson Semantics scene if MP3D semantic is missing. To test semantic loading e2e added integration test that will run only when *.scn test data is available.

How Has This Been Tested

Added the integration test and run it locally with *.scn data:

Running main() from /private/home/maksymets/habitat-sim/src/deps/googletest/googletest/src/gtest_main.cc
[==========] Running 2 tests from 2 test cases.
[----------] Global test environment set-up.
[----------] 1 test from GibsonSceneTest
[ RUN      ] GibsonSceneTest.Basic
[       OK ] GibsonSceneTest.Basic (2 ms)
[----------] 1 test from GibsonSceneTest (2 ms total)

[----------] 1 test from GibsonSemanticSimTest
[ RUN      ] GibsonSemanticSimTest.Basic
[       OK ] GibsonSemanticSimTest.Basic (5451 ms)
[----------] 1 test from GibsonSemanticSimTest (5451 ms total)

[----------] Global test environment tear-down
[==========] 2 tests from 2 test cases ran. (5453 ms total)
[  PASSED  ] 2 tests.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)